In a Group III nitride compound semiconductor light-emitting device such as a blue light-emitting diode, various proposals have been made for obtaining uniform light emission from the whole surface of the device.
For example, in Unexamined Japanese Patent Publication No. Hei. 8-340131 and Unexamined Japanese Patent Publication No. Hei. 10-117017, a p auxiliary electrode is provided radially on an upper surface of a p contact layer to attain uniformity of electric current density injected into the p contact layer. On the other hand, for example, as described in Unexamined Japanese Patent Publication No. 10-275934, a translucent electrode may be stuck on an upper surface of a p-type contact layer so that a p seat electrode is provided thereon. In this example, a p auxiliary electrode is extended from the p seat electrode along sides of the device.
Unexamined Japanese Patent Publication No. Hei. 9-97922 and Unexamined Japanese Patent Publication No. 2000-22210 have disclosed the case where an n auxiliary electrode is provided along sides of the device from an n seat electrode formed in a corner portion of the device, by way of example.
Unexamined Japanese Patent Publication No. 2000-164930 has disclosed a comb-like electrode.
According to the present inventors' examination, it has been found that it is preferable to increase the chip size of light-emitting diodes used in a signal or the like in which high luminance is demanded and light-emitting diodes of one color are collectively used. This is because if the number of light-emitting diodes used can be reduced by increase in chip size, a circuit for evenly distributing an electric current to respective light-emitting diodes can be designed easily and simply as well as the number of steps for assembling the light-emitting diodes can be reduced to attain reduction in production cost.
Therefore, the inventors have made examination again and again to increase the chip size of light-emitting diodes. As a result, the following problems have been found.
Since the resistance of an n contact layer (a layer on which an n electrode is formed) in a light-emitting diode is relatively high, an electric current cannot sufficiently go around to a portion far from the n electrode so that light emission is reduced in the portion. On the other hand, intensive light emission is obtained in a portion near the n electrode, so that light emission becomes uneven on the whole of the device. In a conventional small-size device (300 to 400 μm□) viewed from this point, the portion far from the n electrode was more or less dark, but was limited to a very small area so that the unevenness of light emission was substantially not a large obstacle.
If the chip size becomes large, the amount of an electric current applied to the p seat electrode must be increased when preferable current density injected per unit light-emitting area is to be kept. The current applied to the p seat electrode flows from the p seat electrode into the translucent electrode. If the amount of the current becomes large, there is a high possibility that burning (burning off the translucent electrode in a joint portion by generated Joule heat) may occur between the p seat electrode and the translucent electrode. The area of an interface between the p seat electrode and the translucent electrode is a factor for deciding the amount of the current (permissible current quantity) permitted to be injected into the p seat electrode. It is conceived that the permissible current quantity can increase as the area increases.
If one p seat electrode and one n seat electrode are used in combination when preferred current density is to be secured in an effective light-emitting surface of a large-size chip having an outermost diameter of not smaller than 700 μm, there is a fear that mold resin may be burned by heat generated in a bonding wire portion or the bonding wire itself may be broken by heat unfavorably.